"We are going to have more correlative work planned as a part of the phase-III trial that is coming up," Dr. Yardley added.
In an analysis that was exploratory because follow-up is still short, entinostat was also associated with better overall survival (26.9 vs. 20.3 months; HR, 0.56; P = .027). Additional data with longer follow-up will be reported at the San Antonio Breast Cancer Symposium later this year.
The combination of entinostat and exemestane was well tolerated, with no unexpected safety signals. The most common grade 3/4 adverse events in the entinostat group were fatigue (13%), neutropenia (13%), nausea (5%), and vomiting (5%). The rate of discontinuation because of adverse events was 1% in the placebo group and 11% in the entinostat group.
Dr. Yardley reported that she had no relevant conflicts of interest. Syndax Pharmaceuticals, developer of entinostat, was not among Dr. O’Shaughnessy’s disclosures.